Suburban TBI issues

Hi, everyone. I am new here, and can't seem to figure out where to post my questions...Hopefully, this will be the right forum.

Anyhow, my issue is with my '91 V1500 Suburban 350 TBI. For a few weeks now, my Sub won't start. Generally when it's hot. I know it isn't ignition. Simply fuel delivery. If I spray it with starting fluid, it fires right up.

The first thing I thought of was the temp sensor. Swapped it out, and still won't start. Had to change the starter about a week ago, after it siezed. The alternator a few days ago.

Since I swapped the starter and alternator, it seems less prone to not wanting to start, mostly when it's cold now. Also has a rough idle now. I am sure it isn't the fuel pump, filter or regulator. It runs great at WOT. Doesn't miss a beat.

The plugs, wires and cap are all in good condition. I don't think it is the o2 sensor either. I changed it about 6 months ago when I installed a set of Edelbrock TES shorty headers.

I am not very experienced with fuel injection, so any help would be very greatly appreciated...

Have a helper crank the engine when the problem occurrs and with a flashlight check to see if you can detect any spray from the injector nozzles. It has been a long time but as memory serves there is a start circuit and a run circuit on those. I want to say that the run circuit goes through an oil pressure switch so it shuts off the fuel if it drops oil pressure, but as I said it has been a long time. Also the pick up coil in the distributor and/or the ignition module were somewhat problematic and from time to time caused some wierd symptoms. The connectors on the top of the nozzles were always going bad and we changed them quite frequently but those connectors caused run problems, I dont remember one ever causing a start problem. It just occurred to me that there was a time delay circuit on the fuel pump circuit that ran the pump for a few seconds to pressurize the fuel line on initial start. Take the cap off and listen at the filler pipe while someone cycles the ignition from off to on (not start) and see if the pump runs momentarily. You could also connect a jumper wire to the fuel pump just before a start attempt and determine if it is a pump problem. You have two general possibility's. One, no fuel pressure or two, plenty of fuel pressure but for some reason the nozzles are not triggering. You need to determine which before you can fix the problem. Sorry if this is kind of rambling, but someone once described my mind as a large file drawer marked miscellaneous. you open it up and start pulling things out till you find what you need.

I would check your ground at the intake manifold and make sure he is not floating.

As grumpy old man said, check for your injector pulse....when you start, you should see fule being sprayed into the intake....
If you don't see the injector pulsing fuel, then it could be clogged injectors, or as I said earlier, the ground is floating.
That ground on the intake is for your ECM, and if he doesn't have a closed circuit then he will not tell the injectors when to spray.

Have you checked the fuel filter?? He is located under the truck on the driver side frame.
Get a fuel pressure guage, and make sure you have proper pressure, and as noted above, see if you can hear the pump spin. It should spin initially when the key is turned to pressurize the fuel line.

Going back to the intjectors, if you have not done a rebuild kit on him, you sould go ahead and do that at some point....being that it is a '91, it is prolly time for it.
GP Sorenson has a kit with all you will need...minus the TBI Spray Cleaner.

But check that ground.....it is quick and easy and can save you the hassle of checking other things if he is loose....
Especially if this problem is intermittent.

See, that's the strange thing...It starts whenever it feels like it. For the last couple of days, it's been starting perfectly, but now has a rough idle.

The fuel pump and filter are fine. I know this because it runs fantastic at WOT.

A ground issue doesn't make much sense to me, if it won't start, I just spray it with starting fluid and it fires right up. It doesn't even need a large spray. Just a small squirt, and the injectors kick in...

I did dump a bottle of injector cleaner in the other day. A full bottle is for 21 gallons, and I dumped it into about 16 gallons, which may account for the rough idle, but has started easily ever since.

I am thinking my next step is gonna be plugs and a new o2 sensor.

I will take your advise on all the grounds, though. Might as well be thorough, right?

Grounds are a quick and easy check....and floating grounds make for some really weird problems.

Have you checked your timing??

Regarding the starting fuel, and it starting.
Definitely get someone to start the truck and watch the injectors, you should see mist coming from them when the engine is turned over.

While you have the air cleaner off, you can also look down on the TB and see if the IAC is functioning properly. He sits at about the 10 o'clock position on the TB (12 o'clock being at the firewall, and 6 o'clock being at the radiator).

It might very well be that you need to do a rebuild on the TB.
Have you done that with this one??

Plugs would be worth checking if you have not done them in a while, but I am thinking that is not the issue....

As grumpy mentioned earlier, it could also be your ignition system.
If it is the pickup coil, then you will have to buy a distributor and replace it all at once.
And if you do that, then you might as well get the cap, rotor and ignition coil. Do the whole thing.

I just had problems with my 93 Suburban 350TBI not wanting to idle, but would run if you stepped on the gas, and then it got worse to the point it would not start. But you could start it with starting fluid or by pouring gas down the throttle body. The throttle body was not injecting gas into the motor when you cranked it over. I was told that it could be the ignition control module because it also controls injector pulse. I have replaced this and now it starts, idles and runs fine.

Ignition issues don't make sense, as while it's running (other than rough idle) it doesn't miss a beat! It will outrun my Dad's '95 454 Sub without a second thought. It won't hesitate to lay down a little bit of rubber pulling out on the highway either (not a very easy feat considering it's a factory posi).

The TB was rebuilt a few years ago.

I will absolutely get somebody else to crank it, but I gotta wait 'til it decides not to start again. As I said earlier, it has been starting flawlessly the last couple of days.

The only thing on the ignition that I can think of is the ignition module.

Yes, ignition didnt make sense to me either since it ran perfect once it started. But the ignition control module also control the injector pulse. So it wouldn't idle or idle rough if it did, and eventually wouldn't inject fuel when the engine was cranked over, so then it wouldn't start either. Worth trying it, the module is easy to replace and only cost 40 bucks.

Ignition control modules have been known to go bad on all makes and models of vehicles. When this occurs, there is no spark or a very erratic spark. It is easy to diagnose if this should happen. Use a voltmeter to check for power at the control module. The ignition should be on while checking for power. If there is power, check for a pulsating ground at the module while cranking the engine. This signal is from the computer. If there is a signal, the module is bad. If there is no signal, the computer has an issue with a sensor or itself.

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Either go that route, or get the part and swap it out.....a junkyard may have one.

The next place to look might would be your pickup coil, that will require the whole distributor being replaced on this engine.